1. Technical Field
The invention relates generally to fluid pressure devices and, more particularly, to fluid pressure devices employing a girdle hoop in an elastomeric sleeve. Specifically, the invention relates to a solid steel girdle hoop that reinforces the elastomeric sleeve of an air spring and to its method of installation.
2. Background Information
Flexible elastomeric sleeves are used in various types of fluid pressure systems and devices such as air springs, that are used as both vibrations isolators and actuators. These pneumatic devices or air springs are used in a variety of applications such as cushioning or isolating vibration between moving parts of a land vehicle to absorb vibrations and shock loads impressed on the vehicle axis by the wheels striking an object on the road or dropping into a depression formed in the road surface. Many of these devices also are used as actuators to provide movement between two parts of a machine or piece of equipment.
Most of these air springs have annular beads at the ends of a flexible elastomeric sleeve which form a fluid pressure chamber, with the beads being clamped or crimped onto rigid end members, end plates or pistons. Many such air springs additionally include a girdle hoop annularly disposed within the flexible elastomeric sleeve at approximately the midpoint thereof such that the girdle hoop is interposed between the end plates and substantially parallel therewith. Other air springs use two or more girdle hoops equally spaced along the length of the elastomeric sleeve between the end members. The end members are mounted on spaced portions of a vehicle or other equipment on which the air spring is mounted.
Girdle hoops are presently manufactured of a plurality of thin steel wires that together form a wound cable that has a high strength and is wound into a continuous ring that is then molded within the flexible sleeve to resist extreme outward expansion during heavy shock loading situations.
Examples of such air springs are shown in U.S. Pat. Nos. Re 20,887 and 5,580,033. Other prior art girdle hoops could be hollow tubes or rings such as shown in U.S. Pat. No. 2,999,681. Still another type of prior art girdle hoop is formed of a one-piece non-reinforced plastic ring such as shown in U.S. Pat. No. 4,787,608. Still another type of prior art girdle hoop as shown in a U.K. Patent No. 1198448, uses a girdle hoop formed of a hard rubber.
The annular end beads are internally reinforced with bead hoops that are wound of high strength wire in a fashion similar to that of the girdle hoop and are molded within the ends of the flexible sleeve to assist in maintaining the sleeve beads in an airtight sealing relationship with the end members.
Although these wound or woven reinforcement girdle hoops have been satisfactory for certain purposes, they are expensive and difficult to manufacture. Such hoops also suffer from the potential that one of the high strength wires used to manufacture the hoops might break, with the broken end of the wire often piercing the flexible elastomeric sleeve, thus resulting in a leak in the fluid pressure chamber and ultimate failure of the air spring.
The need thus exists for a girdle hoop that is inexpensive and easy to manufacture, that is strong, and will not puncture the elastomeric sleeve of the air spring. Such a girdle hoop will be manufactured of a solid ring of steel that can be molded into the flexible elastomeric sleeve of an air spring.
In view of the foregoing, an objective of the present invention is to provide a solid steel girdle hoop for a fluid pressure device wherein the girdle hoop is molded into a flexible elastomeric sleeve of an air spring.
Another objective of the present invention is to provide a solid metal girdle hoop that can be installed less costly than prior art girdle hoops in the flexible elastomeric sleeve of an air spring and which is inexpensive to manufacture.
A further objective of the present invention is to provide a solid metal girdle hoop that can be easily installed in the elastomeric sleeve of an air spring and which is stronger and more resistant to breakage or other fracture than many prior art girdle hoops.
Another objective of the present invention is to provide a solid metal girdle hoop that can be installed in the elastomeric sleeve of an air spring to reinforce a fluid pressure chamber formed therein and which obviates the risk that a broken wire will pierce the fluid pressure chamber.
Another objective of the present invention is to provide a solid metal girdle hoop that can be installed in the sleeve of an air spring and which has a lower profile than a stranded girdle hoop of comparable strength.
Another objective of the present invention is to provide an improved girdle hoop that is strong and can flex with the movements of the flexible sleeve into which it is molded and which absorb forces continuously exerted on the flexible sleeve without becoming brittle or breaking and which has sufficient flexibility and material memory permitting the hoop to return to its natural unstressed state.
A still further objective of the present invention is to provide a solid metal girdle hoop which is formed of a cold rolled standard carbon steel within the range of 1018 and 1070, AISI-SAE, and a preferred cross sectional diameter within the range of 0.170 and 0.193 inches for a ring having an external diameter of approximately 4 inches.
A further objective of the present invention is to provide such a solid metal girdle hoop in which the cross sectional thickness is substantially within the range of 4% to 5% of the outer diameter of the hoop.
Still another objective of the present invention is to provide an improved method of manufacturing the solid metal girdle hoop and installing it in the air spring.
These and other objectives and advantages are obtained by the improved girdle hoop of the present invention, the general nature of which may be stated as including a fluid pressure device including a pair of end members and an intervening elastomeric sleeve forming a fluid pressure chamber therein; and a girdle hoop disposed within said sleeve between said end members, said girdle hoop being formed of a solid steel material.
These and other objectives and advantages are obtained by the improved method for manufacturing an air spring containing a girdle hoop formed of a solid metal material, said method comprising the steps of forming a length of a solid metal material into a substantially toroidal member; bonding said toroidal member into an elastomeric sleeve of material; and mounting the elastomeric sleeve between a pair of spaced end members.